The present invention relates generally to aircraft gas turbine engines, and, more specifically, to an intake therefor.
In a typical turboprop aircraft, a gas turbine engine has an output drive shaft joined to a reduction gearbox for powering propellers. The engine and gearbox are contained in a nacelle which provides an aerodynamically smooth interface for minimizing drag during flight operation of the aircraft. The gearbox is a relatively large component mounted forwardly of the engine, and therefore a suitable air intake is required for bypassing the gearbox and suitably channeling a portion of the propeller air into the engine wherein it is compressed and mixed with fuel and ignited for generating hot combustion gases which power the engine and in turn the propellers.
The aircraft inlet must be suitably designed for channeling the propeller air into the engine with minimal aerodynamic losses. Since the gearbox obstructs direct access to the engine inlet, the air intake is laterally offset from the engine and its coaxial drive shaft which complicates the aerodynamic design thereof. The resulting air intake is typically S-shaped for turning the air from an initially axial direction radially inwardly toward the engine inlet where again it is turned axially for being channeled thereto. The profile of the turning intake must be carefully selected to avoid undesirable flow separation of the channeled air which would create pressure losses. And, the intake air must also be suitably channeled to the engine inlet with a circumferentially uniform profile for ensuring effective operation of the engine.
A conventional air intake is also typically configured for diffusing the propeller air for increasing its pressure or reducing the velocity thereof, which is made more complex in view of the S-shaped intake flowpath. The resulting intake designs are typically relatively large for providing effecting diffusion without undesirable flow separation. The design is also relatively axially long which increases the wetted surface area of the nacelle, and corresponding aerodynamically drag therefrom, as well as increasing the overall weight of the aircraft. The larger intake can therefore ingest relatively large birds or other foreign objects, which requires yet further complexity in the intake and engine design for ensuring effective operation without undesirable damage in the event of bird ingestion.